1. Field of the Invention
The present invention relates to a method for estimating channel, and more particularly, to a method and an apparatus for channel estimation.
2. Discussion of the Related Art
In the world of cellular telecommunications, those skilled in the art often use the terms 1G, 2G, and 3G. The terms refer to the generation of the cellular technology used. 1G refers to the first generation, 2G to the second generation, and 3G to the third generation.
1G refers to the analog phone system, known as an AMPS (Advanced Mobile Phone Service) phone systems. 2G is commonly used to refer to the digital cellular systems that are prevalent throughout the world, and include CDMAOne, Global System for Mobile communications (GSM), and Time Division Multiple Access (TDMA). 2G systems can support a greater number of users in a dense area than can 1G systems.
3G commonly refers to the digital cellular systems currently being deployed. These 3G communication systems are conceptually similar to each other with some significant differences.
In a wireless cellular communication system, it is important to device schemes and techniques that increase the information rate and improve the robustness of a communication system under the harsh conditions of the wireless environment. The wireless communication channel is the source of various impairments to a digital communication system, due to factors such as the relative mobility of transmitter and receiver, multipath propagation, interference from other users of the frequency spectrum, and time-variation which is more commonly known as fading.
For straightforward communication system design, an ideal channel is one that exhibits constant frequency response over the frequency band, and thus produces undistorted replica of the transmitted signal at the receiver, possibly delayed and scaled. To put differently, if the transmitted signal s(t) has an equivalent low pass frequency representation S(f), occupying total bandwidth W, then the equivalent low pas frequency response C(f) of an ideal channel is C(f)=|C(f)|·ej∠C(f)=C·ej2πtf for all frequencies in the band W of interest. If s(t) is processed through the above ideal channel, the received signal would be r(t)=C·s(t−τ).
Unfortunately, the real world transmission (e.g., mobile wireless channel) has imperfections which impair reliable transmission of information. Consequently, the task of the receiver becomes more complicated when those impairments are unknown beforehand and/or time variant.